That would be the day the Democrats and Republicans turned their backs on the Constitution of the United States.
From Reason Online's article on the subject:

We must, and we shall, set the tide running again in the cause of freedom. And this party, with its every action, every word, every breath, and every heartbeat, has but a single resolve, and that is freedom.
Barry Goldwater, accepting the 1964 Republican presidential nomination

This year's Republican National Convention had a different theme for each day. Monday was "Serving a Cause Greater than Self." Tuesday was "Service," Wednesday was "Reform," and Thursday was "Peace."

So what was missing? Only what used to be held up as the central ideal of the party. The heirs of Goldwater couldn't spare a day for freedom.

Neither could the Democrats. Their daily topics this year were "One Nation," "Renewing America's Promise," and "Securing America's Future." The party proclaimed "an agenda that emphasizes the security of our nation, strong economic growth, affordable health care for all Americans, retirement security, honest government, and civil rights." Expanding and upholding individual liberty? Not so much.

Forty-four years after Goldwater's declaration, it's clear that collectivism, not individualism, is the reigning creed of Republicans as well as Democrats. Individuals are not valuable and precious in their own right but as a means for those in power to achieve their grand ambitions.

You will scour the presidential nominees' acceptance speeches in vain for any hint that your life is rightfully your own, to be lived in accordance with your beliefs and desires and no one else's. The Founding Fathers set out to protect "life, liberty and the pursuit of happiness," but Barack Obama has a different idea.

The "essence of America's promise," he declared in Denver, is "individual responsibility and mutual responsibility"—rather than, say, individual freedom and mutual respect for rights. The "promise of America," he said, is "the fundamental belief that I am my brother's keeper; I am my sister's keeper."

In reality, that fundamental belief is what you might call the promise of socialism. What has set this country apart since its inception is not the notion of obligations but the notion of rights.

"All previous systems had regarded man as a sacrificial means to the ends of others, and society as an end in itself," wrote the novelist and philosopher Ayn Rand. "The United States regarded man as an end in himself, and society as a means to the peaceful, orderly, voluntary co-existence of individuals."